In general, a passenger airbag device is stored in an instrument panel of a vehicle. When the vehicle stops abruptly due to a collision or the like, the passenger airbag device receives a supply of gas from an inflator attached to the airbag device, is inflated through a deployment door provided in a top surface of the instrument panel, and is deployed in a space between a windshield (front window) and an occupant seated in a passenger's seat, thereby protecting the occupant seated in the passenger's seat.
This passenger airbag device is in contact with the windshield and the top surface of the instrument panel when it is inflated and deployed, whereby the behavior thereof is stabilized. However, if the instrument panel is designed to have a small portion on the occupant side, with respect to an installation position of the airbag device, in the top surface of the instrument panel, the behavior of a cushion (bag) of the airbag device is unstable.
To solve this problem, the volume of the cushion has to be increased to fill a space surrounded by the occupant, the windshield of the vehicle, and the instrument panel, thereby reliably receiving the occupant. Thus, cushions of passenger airbag devices tend to have large volumes.
A cushion of an airbag device having a large volume requires a lager amount of base fabric constituting the cushion. Furthermore, for quick inflation and deployment of the cushion having a large volume, a high-power inflator is needed.
However, because high-power inflators are expensive, the use of such an inflator increases the total cost. In addition, the strength of the airbag device and components thereof also needs to be increased to cope with the power of the inflator, resulting in a problem in that the weight of the airbag device increases.
To overcome this problem, a passenger airbag device, in which the volume of the cushion is reduced so that it can be quickly inflated by a relatively low-power inflator while exhibiting a sufficient impact-absorbing ability, has been proposed (see PTL 1).
FIG. 7 shows an example of such a passenger airbag device.
A cushion 100 of this passenger airbag device includes an occupant-facing surface 102 at its front end, and a windshield-facing surface 104 at an upper surface thereof. The occupant-facing surface 102 and the windshield-facing surface 104 are configured to be connected by an inner member 106. Therefore, when an inflator 112 is activated to discharge gas, the occupant-facing surface 102 is inflated toward the occupant due to the pressure of the gas, and a middle portion of the windshield-facing surface 104 in the top-bottom direction is pulled by the occupant-facing surface 102 through the inner member 106 and is deployed in a shape recessed toward the inner side of the cushion away from the windshield 122. With this configuration, the volume of the cushion 100 is reduced.
Similarly, although it is not necessarily aimed at reducing the volume of the cushion of an airbag device, a passenger airbag device having a cushion composed of a first inflation portion, which constitutes an occupant protection portion that can interfere with an occupant seated in a passenger's seat, and a second inflation portion, which is inflated between the first inflation portion and the instrument panel with the inflation gas flowing from the first inflation portion when the first inflation portion is inflated, is known (see PTL 2).
However, because the cushion 100 of the airbag device disclosed in PTL 1 is reduced in volume on the windshield side, the behavior of the cushion when deployed may be less stable. Furthermore, because a separate member, i.e., the inner member 106, is required and because an operation to attach the inner member 106 to the occupant-facing surface 102 and the windshield-facing surface 104 is required, the fabrication process becomes complex, resulting in another problem in that the cost is increased compared with a cushion formed by simply joining the base fabric pieces.
Furthermore, although the passenger airbag device disclosed in PTL 2 has a more complex structure than that disclosed in PTL 1 and requires high cost, it does not always succeed in reducing the volume of the cushion of the airbag device.
If the overall volume of the cushion is simply reduced, as shown in, for example, FIG. 8, the cushion 10 starts to be inflated and deployed from the top surface of the instrument panel 20, is deployed along the top surface of the instrument panel 20 toward the occupant, without completely filling the space between the instrument panel 20 and the windshield 25 (see FIGS. 8A to 8D). In the subsequent process of being inflated and deployed, the cushion 10 temporarily hangs down in front of the instrument panel 20 (see FIG. 8E) but is then erected away from the panel surface upon further application of the gas pressure from the inflator (see FIG. 8F). Thus, the behavior of the cushion is unstable, and sufficient support may not be provided because the support position of the cushion when the occupant moves forward into the cushion is unstable.